This invention relates to a high-voltage discharge lamp and, more particularly, to a high-voltage discharge lamp in which it is possible to prevent a quartz-glass bulb from bursting at the time of high-temperature thermal processing or at the time of operation.
A high-voltage discharge lamp according to the prior art has a structure of the kind shown in FIG. 6, by way of example. Specifically, a high-voltage discharge lamp 1 includes a quartz-glass bulb 2, which comprises an enlarged portion 21 that provides a light-emitting space and a seal portion 22, and a pair of opposing electrodes (an anode 3 and cathode 4) disposed within the glass bulb 2. The anode 3 and cathode 4 are joined to the molybdenum foils 5 and 5xe2x80x2, respectively, by means such as welding. Further, the molybdenum foils 5, 5xe2x80x2 are hermetically sealed within the bulb 2 at the seal portions 22 thereof. The enlarged portion 21 having the light-emitting space is filled with a discharge gas or the like.
Coils 6, 6xe2x80x2 comprising a material such as tungsten, tantalum or molybdenum are wound on the anode 3 and cathode 4, respectively, on or near the joints between these electrodes and the molybdenum foils 5, 5xe2x80x2. By winding the coils 6, 6xe2x80x2 on the electrodes, stress applied to the glass bulb 2 owing to thermal expansion of the electrodes 3, 4 can be mitigated even in a case where thermal processing is applied at high temperature or when the high-voltage lamp is operated. As a result, it is possible to prevent cracking at the portions where the electrodes 3 and 4 contact the glass bulb 2.
In the course of the investigations toward the present invention, it has turned out that there is much to be desired in the art.
When the coils are wound on the electrodes, however, protrusions are produced at the leading and trailing ends of the coils and the protrusions scratch the glass bulb. As a consequence, the glass bulb tends to crack. Further, when the coils are wound on the electrodes, a load (tensile force) acts upon the electrodes. If an electrode has a diameter of 0.6 to 0.8 mm, therefore, the electrode is deformed. It is technically very difficult to eliminate these protrusions and to prevent the deformation of the electrodes. Furthermore, a high-voltage discharge lamp of this kind cannot discharge stably and sufficiently stable brightness cannot be obtained.
Accordingly, an object of the present invention is to provide a high-voltage discharge lamp in which it is possible to eliminate the scratching of a quartz-glass bulb and the deformation of electrodes,and to mitigate thermal stress at the time of high-temperature thermal processing and high-voltage discharge operation, as a result of which the occurrence of cracking can be prevented and sufficiently stable brightness can be obtained.
As a result of extensive research, the inventor has devised a high-voltage discharge lamp in which the joint, as well as the vicinity thereof, between at least one electrode and molybdenum foil is covered by a cylindrical member the outer and/or inner surface of which has slits, or by a mesh-like member. The inventor has found that such a high-voltage discharge lamp will no longer have its quartz-glass bulb scratched, that the electrode will no longer be deformed because it is unnecessary for the joint or the vicinity thereof to have a hermetic seal, that it is possible to mitigate thermal stress at the time of high-temperature thermal processing or high-voltage discharge operation, thereby preventing the occurrence of cracking, and that sufficiently stable brightness is obtained. The present invention has been perfected on the basis of these findings.
Specifically, according to the present invention, the foregoing object is attained by providing a high-voltage discharge lamp having a bulb made of quartz glass, a pair of electrodes and molybdenum foils, wherein the pair of electrodes are arranged so as to oppose each other and are joined to respective ones of the molybdenum foils, and the bulb and molybdenum foils are hermetically sealed at seal portions of the bulb, characterized in that joints, as well as the vicinities thereof, between the pair of electrodes and the molybdenum foils are covered by cylindrical members having slits on an outer surface and/or an inner surface thereof.
According to another aspect of the present invention, the foregoing object is attained by providing a high-voltage discharge lamp having a bulb made of quartz glass, a pair of electrodes and molybdenum foils, wherein the pair of electrodes are arranged so as to oppose each other and are joined to respective ones of the molybdenum foils, and the bulb and molybdenum foils are hermetically sealed at seal portions of the bulb, characterized in that joints, as well as the vicinities thereof, between the pair of electrodes and the molybdenum foils are covered by mesh-like members.